Date: Fri, 11 Apr 2003 01:55:31 -0400 (EDT) From: Daniel Eischen <eischen@pcnet1.pcnet.com> To: David Xu <davidxu@freebsd.org> Cc: freebsd-threads@freebsd.org Subject: Re: patch for %gs saving Message-ID: <Pine.GSO.4.10.10304110135540.23482-100000@pcnet1.pcnet.com> In-Reply-To: <008001c2ffe8$056584f0$f001a8c0@davidw2k>
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On Fri, 11 Apr 2003, David Xu wrote: > Here is the patch for kernel to save %gs, > it works well on my machine. > http://people.freebsd.org/~davidxu/i386_gs.diff Thanks, I'll give it a go. > Daniel, is this the reason in your libpthread > patch that doesn't use getcontext syscall ? No, we already had userland versions of getcontext() so I simply reused them to avoid the system call. That's why THR_GETCONTEXT is a macro; it can be defined to be getcontext() for those archs that don't have userland versions and want to use the system call instead. Note that we still need userland versions of _thread_switch() and _thread_enter_uts() anyways, so writing a userland [gs]etcontext() is probably pretty simple once you have those. Plus, when you get a context in order to make a context for a new thread, you still can't rely on %gs because it may be scheduled on another KSE or the thread could be a scope system thread in which case it be scheduled in another KSEG. So the current %gs isn't necessarily correct for a new thread. Hmm, this raises a good point. Once you set up a thread to run a signal handler, the %gs register has already been set. We have to be sure that the interrupted context and the thread's new (signal) context both have the same %gs and that it runs on the correct KSE. Either that, or we have to be able to change the contexts to be the correct %gs before running the thread and invoking the handler. -- Dan Eischen
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